Analog to digital help

[DuWong]

Is there a way to use an arduino to be able to read an analog signal of 0 to +30V? I know the arduino can only go up to +5v, I think it would it be possible to voltage divide the analog signal but wouldn't that lose a lot of precision? Or how could I use another circuit to convert it from analog to digital?

[Zero999]

Yes, use a potential divider to reduce the voltage. There will be some loss of precision, but 1% resistors are normally good enough. In any case, there's no point in exceeding the specifications of the ADC or reference.

Here's a site with a handy potential divider calculator tool. Obviously the results can be multiplied by a factor of 10, to get the desired input impedance.
http://sim.okawa-denshi.jp/en/teikokeisan.htm

One thing to note is that the ADC takes a current spike, when a sample is taken, as the sample and hold capacitor charges. If the potential divider's output impedance is very high, this can upset the reading. One solution, to minimise loading on the circuit being measured, is to keep the potential divider's resistor values high and add a capacitor between the ADC's input and 0V. Unfortunately this reduces the bandwidth, so is only useful for low frequency signals.

[Shock]

Opamp based solution here.

https://electronics.stackexchange.com/questions/266737/high-voltage-sampling-with-microcontroller-potential-divider-affecting-signal

[Zero999]

Opamp based solution here.

https://electronics.stackexchange.com/questions/266737/high-voltage-sampling-with-microcontroller-potential-divider-affecting-signal

Yes, that will work, just ensure the common mode input range of the op-amp isn't being exceeded, so R401 might need to be skipped, to ensure the supply voltage isn't higher, than the inputs. In this case, the input signal can be up to 30V, so you need an op-amp with a rail-to rail input. A quick look through the RS catalogue yielded the following: LM7322, LT1638, ADA4091, LT1490A.